Indium Tin Oxide Anode Research Articles

Algae Biofilm on Indium Tin Oxide Electrode for Use in Biophotovoltaic Platforms

Algae are amongst the most photosynthetically efficient organisms harnessing solar energy for all its metabolic life-supporting activities. The solar energy is transformed into chemical energy in a normally wasteful process. In this study, this excess wasted energy may be directed towards electricity generation in a biophotovoltaic platform. This is a new approach in renewable energy production from algae. As an initial step, algal biofilms are established on indium tin oxide (ITO) anodes. Two microalgae, the unicellular Chlorella UMACC 313 and the filamentous Spirulina UMACC 159 were used to form biofilm on ITO anodes under three different treatments (T1: unmodified smooth surface , T2: modified surface etched with interval of 2.5 mm between lines and T3: modified surface etched with interval of 1 mm between lines). Results show significantly higher biofilm coverage on the etched anodes compared to the smooth ones. Anodes of T3 registered the highest biofilm coverage of 99.46% for Chlorella. For Spirulina, highest biofilm coverage (80.70%) was observed on T2 anodes. The increase in biofilm coverage successfully resulted in increase of photosynthetic efficiency for both strains. Spirulina registered the highest maximum relative electron transport rate at 153.507 μmol electrons m-2s-1 compared to Chlorella (140.796 μmol electrons m-2s-1). This was correlated to pigment content. Biofilms established on the ITO anodes and the resulting high rate of photosynthetic efficiency achieved in these experiments are expected to enable electrical energy production from biophotovoltaic platforms.

Semiconductor to metal transition in degenerate ZnO: Al films and the impact on its carrier scattering mechanisms and bandgap for OLED applications

Temperature dependent Hall measurements revealed that ionized impurity scattering was the dominant mechanism in sputter deposited, degenerate, aluminum doped zinc oxide (AZO) films up to ~530 nm thickness, and a semiconductor to metal transition was observed when thickness was further increased. With the increase in film thickness, the mobility and conductivity also increased from 6.70 to 18.7 cm2 V−1 s−1 and 1.83 × 102–8.28 × 102 (Ω cm)−1, respectively. However, this was accompanied by a larger than 0.2 eV Burstein–Moss blue-shift of the interband absorption edge determined from absorption spectra. The movement of the Fermi level further into the conduction band that accompanies the Burstein–Moss shift results in a corresponding workfunction decrease of the films. This means that the interface barrier for hole injection in anode applications such as organic light emitting diodes (OLEDs) becomes larger, which translates into higher turn-on voltages and lower current and power efficiencies compared to indium tin oxide anodes. It is suggested that improving conductivity through mobility increases, and increasing workfunction through surface functionalization may improve the prospects of AZO films in OLEDs and other applications where in addition to conductivity and transparency, workfunction is also critical.

Low-cost electrochemical treatment of indium tin oxide anodes for high-efficiency organic light-emitting diodes

We demonstrate a simple low-cost approach as an alternative to conventional O2 plasma treatment to modify the surface of indium tin oxide (ITO) anodes for use in organic light-emitting diodes. ITO is functionalized with F− ions by electrochemical treatment in dilute hydrofluoric acid. An electrode with a work function of 5.2 eV is achieved following fluorination. Using this electrode, a maximum external quantum efficiency of 26.0% (91 cd/A, 102 lm/W) is obtained, which is 12% higher than that of a device using the O2 plasma-treated ITO. Fluorination also increases the transparency in the near-infrared region.

Device Performances of Organic Light-Emitting Diodes with Indium Tin Oxide, Gallium Zinc Oxide, and Indium Zinc Tin Oxide Anodes Deposited at Room Temperature

Thin films of Indium tin oxide (ITO), Gallium zinc oxide (GZO), and Indium zinc tin oxide (IZTO) were deposited on glass substrates by pulsed direct current magnetron sputtering at room temperature. The structural, optical, and electrical properties of the films were investigated towards evaluating their applications as flexible anodes. IZTO films exhibited the lowest resistivity (6.3 x 10(-4) Omega cm). Organic light-emitting diodes (OLEDs) were fabricated using the ITO, GZO, and IZTO films as anode layers. The turn-on voltages at a current density of 4.5 mA/cm2, 5.5 mA/cm2, 6.5 mA/cm2 were 5.5 V, 13.7 V, and 4.7 V for the devices with ITO, GZO, and IZTO anodes, respectively. The best performance was observed with the IZTO film, indicating its suitability as an alternative material for conventional ITO anodes used in OLEDs and flexible displays.

Enhanced and balanced efficiency of white bi-directional organic light-emitting diodes

We report on the characteristics of enhanced and balanced white-light emission from bi-directional organic light-emitting diodes (BiOLEDs) enabled by the introduction of micro-cavity effects. The insertion of an additional metal layer between the indium tin oxide anode and the hole transporting layer results in similar light output of our BiOLEDs in both top and bottom direction and in reduced distortion of the electroluminescence spectrum. Furthermore, we find that by utilizing MC effects, the overall current efficiency can be improved by 26.2% compared to that of a conventional device.

Preparation of indium tin oxide anodes using energy filtrating technique for top-emitting organic light-emitting diode

Indium tin oxide (ITO) anodes were deposited by an improved magnetron sputtering technique (energy filtrating magnetron sputtering technique, EFMS) for top-emitting organic light-emitting diodes (TOLEDs). The phases, surface morphologies and optical properties were examined by X-ray diffraction (XRD), scanning electron microscope (SEM), atomic force microscopy (AFM) and spectroscopic ellipsometer. The sheet resistances were measured by the sheet resistance meter. The electrical properties were tested by the Hall measurement system. The electro-optic characteristics were examined by a special home-made measurement system. Results indicated that ITO anode deposited by EFMS had a more uniform and smoother surface with smaller grains. ITO film was prepared with the electrical property of the lowest resistivity (4.56×10−4Ωcm), highest carrier density (6.48×1020cm−3) and highest carrier mobility (21.1cm2/V/s). The average transmissivity of the ITO film was 87.0% in the wavelength range of 400–800nm. The TOLEDs based on this ITO anode had a lower turn-on voltage of 2V (>0.02mA/cm2), higher current density of 58.4mA/cm2 at 30V, higher current efficiency of 1.374cd/A and higher luminous efficiency of 0.175lm/W. The possible mechanism of the technique was discussed in detail.

Bi‐directional organic light‐emitting diodes with nanoparticle‐enhanced light outcoupling

AbstractAn effective method is presented for enhancing the outcoupling efficiency of translucent/bi‐directional organic light‐emitting diodes (TL/BD‐OLEDs) with a bottom indium tin oxide (ITO) anode and a top cathode comprised of a thin Ag layer covered with an organic capping layer. Upon insertion of a nanoparticle (NP)‐based scattering layer (NPSL) between the substrate and the ITO anode, the TL/BD‐OLEDs exhibit significantly enhanced external quantum efficiency (EQE) in both emission directions. Furthermore, the NPSL improves the color stability of the TL/BD‐OLEDs over a wide range of viewing angles. Simulations based on geometrical and statistical optics are performed to elucidate the mechanism by which the efficiency is enhanced and to establish strategies for further optimization. Simulations performed on the scattering layers with varying NP volume percentage reveal that the bottom‐side emission is governed by competition between waveguide‐mode extraction and backward scattering by NPs in the film, while the top‐side emission is largely dominated by the latter. Optimized bi‐directional OLEDs achieve a 1.64‐fold enhanced EQE compared to reference devices without NPSL.

Effects of surface treatment of ITO anode layer patterned with shadow mask technology on characteristics of organic light-emitting diodes

We investigated the effects of various surface treatments of indium tin oxide (ITO) on the electrical and optical characteristics of organic light-emitting diodes (OLEDs). A 150-nm-thick ITO anode layer was patterned directly with a shadow mask during the sputtering process without the use of a conventional photolithography patterning method. The sputtered ITO layer was subjected to thermal and oxygen plasma treatments to reduce the sheet resistance and improve surface roughness. The thermal treatment was performed for 1h at temperatures of 250 and 380°C, which were chosen so that the glass substrates would not deform from thermal damage. The measured sheet resistance decreased from 30.86Ω/sq for the as-sputtered samples to 8.76Ω/sq for the samples thermally treated at 380°C for 1h followed by oxygen plasma treatment. The root-mean-square surface roughness measured by atomic force microscopy considerably decreased to 3.88nm with oxygen plasma treatment. The thermal treatment considerably decreased the sheet resistance of the ITO anode layer patterned with the shadow mask. The spike-like structures that are often formed and observed in shadow mask-patterned ITO anode layers were almost all removed by the oxygen plasma treatment. Therefore, a smooth surface for shadow mask-patterned ITO layers with low sheet resistance can be obtained by combining thermal and oxygen plasma treatments. A smooth surface and low sheet resistance improves the electrical and optical characteristics of OLEDs. The surface-treated ITO layer was used to fabricate and characterize green phosphorescent OLED devices. The typical characteristics of OLED devices based on surface-treated shadow mask-patterned ITO layers were compared with those fabricated on untreated and photolithography-patterned ITO layers to investigate the surface treatment effects. The OLED devices fabricated by thermal treatment at 380°C for 1h followed by oxygen plasma treatment for 180s showed the highest luminance and current density. Furthermore, the leakage current that might be induced by the rough ITO surface was dramatically reduced to 0.112mA/cm2. Our study showed that the shadow mask-patterned ITO anode layer treated by heat and plasma and having a low sheet resistance and surface roughness yielded excellent electrical and optical properties for OLEDs compared to those based on an untreated ITO layer. The fabricated OLED devices using the surface-treated shadow mask-patterned ITO layer exhibited comparable characteristics to those obtained from a conventional photolithography-patterned ITO anode.

Performance improvement of organic light emitting diode with aluminum oxide buffer layer for anode modification

A thin Al2O3 insulating buffer layer deposited on indium tin oxide (ITO) anode by atomic layer deposition has been investigated for organic light-emitting diodes (OLEDs). With an optimal thickness of 1.4 nm and low density of structural defects of the Al2O3 film, the OLEDs current efficiency and power efficiency were simultaneously improved by 12.5% and 23.4%, respectively. The improvements in both current and power efficiency mean lower energy loss during holes injection process and better balanced charge injection. To understand the mechanism behind the enhanced performance of OLED by the buffer layer, a series of Al2O3 films of different thicknesses were deposited on ITO anode and characterized. The roughness, sheet resistance, and surface potential (EF′) of the Al2O3 modified ITO were characterized. Also, the properties of Al2O3 films were investigated at the device level. It is believed that the block of holes injection by the Al2O3 buffer layer makes more balanced carrier density in the emitting layer, thus enhances the current efficiency. Although less number of holes are injected into OLED due to the Al2O3 buffer layer, quantum tunneling through the ultra-thin buffer layer play an important role in contributing to the holes injection, which avoids crossing the interface barrier, resulting in less energy consumed and power efficiency enhanced.

Work‐Function Engineering of Graphene Anode by Bis(trifluoromethanesulfonyl)amide Doping for Efficient Polymer Light‐Emitting Diodes

Graphene has been considered to be a potential alternative transparent and flexible electrode for replacing commercially available indium tin oxide (ITO) anode. However, the relatively high sheet resistance and low work function of graphene compared with ITO limit the application of graphene as an anode for organic or polymer light‐emitting diodes (OLEDs or PLEDs). Here, flexible PLEDs made by using bis(trifluoromethanesulfonyl)amide (TFSA, [CF3SO2]2NH) doped graphene anodes are demonstrated to have low sheet resistance and high work function. The graphene is easily doped with TFSA by means of a simple spin‐coating process. After TFSA doping, the sheet resistance of the TFSA‐doped five‐layer graphene, with optical transmittance of ≈88%, is as low as ≈90 Ω sq−1. The maximum current efficiency and power efficiency of the PLED fabricated on the TFSA‐doped graphene anode are 9.6 cd A−1and 10.5 lm W−1, respectively; these values are markedly higher than those of the PLED fabricated on pristine graphene anode and comparable to those of an ITO anode.

Fabrication of an organic light-emitting diode inside a liquid crystal display

The fabrication of a hybrid device architecture fully integrating a transparent organic light-emitting diode (OLED) and a liquid crystal display (LCD) within two glass substrates is reported in this study. The transparent OLED was fabricated on the inner surface of the glass substrate. Twisted nematic liquid crystal (LC) materials were used to fill the space between the two glass substrates. The OLED was driven by an indium-tin oxide (ITO) anode on the glass substrate and a thin bi-metal (Al/Ag) cathode, which also served as the electrode of the LCD. The other electrode for the LCD-mode operation was the ITO on the other glass substrate. A commercially available ultraviolet (UV)-curable resin was spun onto the thin Al/Ag as the passivation layer to protect the OLED from attacks by the following polyimide layer (serving as the alignment layer of the LCD), rubbing process and LC materials. In this device structure, the electrical characteristic of the OLED-mode operation was almost the same as that of the control device. Current efficiency (in terms of cd/A) of the hybrid device from top-emission (towards the LCD) decreased by 26.5% due to optical interference effect, whereas efficiency from bottom-emission remained the same. The driving voltage of the LCD-mode operation increased by 1.6V due to the insertion of the passivation layer between the two electrodes. The contrast ratio decreased from 150 to 25 due to the reflection of the thin Al/Ag layer. Compared with that of the control device, the storage lifetime of the OLED increased as a result of filling the encapsulated cavity with LC materials, which helped repel ambient water and oxygen.

Investigation of recombination dynamics for indium tin oxide-free organic photovoltaics by illumination dependence study

Highly conductive poly(3,4-ethylene-dioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) is used as an anode material to construct flexible organic photovoltaics on plastic, poly(ethylene naphthalate) (PEN) substrates with a device structure of PEN/modified PEDOT:PSS/poly(3-hexylthiophene):phenyl-C61-butyric acid methyl ester (P3HT:PCBM)/Al. The indium tin oxide (ITO)-free flexible device exhibits a 20% increase in power conversion efficiency under 1 sun with a higher open circuit voltage (0.67 V) compared to that of the reference device having an ITO anode on a glass substrate (0.54 V). A study of the different recombination mechanisms within these two device structures is carried out by comparing the illumination responses of open circuit voltage as well as short circuit current. The results explain the varying trend of fill factor and power conversion efficiency with respect to the light intensity and suggest that a bimolecular recombination mechanism is dominant in the ITO-free devices.

Highly efficient fully flexible indium tin oxide free organic light emitting diodes fabricated directly on barrier-foil

We present a simple method for the fabrication of highly conductive and fully flexible metal/polymer hybrid anodes for efficient organic light emitting diodes (OLEDs). By incorporating ultra-thin metal grids into a conductive polymer, we fabricated anodes with very low sheet resistances and high transparency. After optimizing the metallic grid, OLEDs with these hybrid anodes are superior to OLEDs with standard indium tin oxide (ITO) anodes in luminous efficacy by a factor of ~2. Furthermore, the sheet resistance can be reduced by up to an order of magnitude compared to ITO on polyethylene terephthalate (PET). The devices show a very low turn-on voltage and the hybrid anodes do not change the emissive spectra of the OLEDs. In addition, we fabricated the anodes directly on a barrier foil, making the double sided encapsulation of a typically used PET-substrate unnecessary.

Improved photovoltaic characteristics of organic cells with heterointerface layer as a hole-extraction layer inserted between ITO anode and donor layer

We have fabricated an improved organic photovoltaic (OPV) cell in which organic heterointerface layer is inserted between indium-tin-oxide (ITO) anode and copper-phthalocyanine (CuPc) donor layer in the conventional OPV cell of ITO/CuPc/fullerene (C60)/bathophenanthroline (Bphen)/Al to enhance the power conversion efficiency (PCE) and fill factor (FF). The inserted ITO-buffer layer consists of electron-transporting layer (ETL) and hole-transporting layer (HTL). We have changed the ETL and HTL materials variously and also changed their layer thickness variously. It is confirmed that ETL materials with higher LUMO level than the work function of ITO give low PCE and FF. All the double layer buffers give higher PCE than a single layer buffer of TAPC. The highest PCE of 1.67% and FF of 0.57% are obtained from an ITO buffer consisted of 3nm thick ETL of hexadecafkluoro-copper-phthalocyanine (F16CuPc) and 3nm thick HTL of 1,1-bis-(4-methyl-phenyl)-aminophenylcyclohexane (TAPC). This PCE is 1.64 times higher than PCE of the cell without ITO buffer and 2.98 times higher than PCE of the cell with single layer ITO buffer of TAPC. PCE is found to increase with increasing energy difference (ΔE) between the HOMO level of HTL and LUMO level of F16CuPc in a range of ΔE<0.6eV. From the ΔE dependence of PCE, it is suggested that electrons moved from ITO to the LUMO level of the electron-transporting F16CuPc are recombined, at the F16CuPc/HTL-interface, with holes transported from CuPc to the HOMO level of HTL in the double layer ITO buffer ETL, leading to efficient extraction of holes photo-generated in CuPc donor layer.

High performance semitransparent phosphorescent white organic light emitting diodes with bi-directional and symmetrical illumination

A semitransparent white organic light-emitting diode (WOLED) is produced based on a blue phosphorescence from iridium(III)[bis(4,6-difuorophenyl)-pyridinato-N,C2] picolinate and an orange phosphorescence from bis(2-(9,9-diethyl-9H-fluoren-2-yl)-1-phenyl-1H-benzoimidazol-N,C3) iridium(acetylacetonate). In this work, a hole-transporting layer of N,N′-diphenyl-N,N′-bis(1-naphthylphenyl)-1,1′-biphenyl-4,4′-diamine (NPB) and an electron-transporting layer of 3,5,3″,5″-tetra-3-pyridyl-[1,1′;3′,1″] terphenyl (B3PyPB) were used. B3PyPB has high electron mobility and a high triplet energy level. The use of B3PyPB helps to reduce the triplet quenching and also to confine the charge recombination in the emissive region of a single-host two-color WOLED. A bi-layer Ag (10 nm)/MoO3 (2.5 nm)-modified indium tin oxide anode and a cathode of Al (1.5 nm)/Ag (15 nm)/NPB (50 nm) were employed. The semitransparent WOLEDs thus developed have perfect symmetrical, bi-directional illumination characteristics, and the weak angular dependent EL emission spectra, which are beneficial for application in planar diffused lighting.

Stackable spectral-sensitive conductive films based on cyanine aggregates via an inkjet method

Abstract In this work, wavelength sensitive organic bulk-hetero photodiodes were fabricated by a piezoelectric inkjet method based on the J-type aggregates of cyanine dye molecules doped into poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate) thin films on indium tin oxide anodes. The cyanine dye concentration in the inkjet printed films was optimized and the J-aggregate formation during the drying process was investigated by local absorption spectra. It was found that at lower dye concentrations, not only the J-aggregate formation but also the radiation sensitivities of the films were improved significantly. Moreover, the stacking of the cyanine dye – poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate) spots demonstrated the linear increase on the optical density and film thickness without deteriorating the J-aggregate formation, indicating their potential in application as narrow band filters.

Enhanced performance in polymer solar cells by the use of a halogenated indium tin oxide anode

Use of a halogenated, surface-modified indium tin oxide (ITO) anode was found to enhance the photovoltaic performance of a bulk heterojunction (BHJ) polymer solar cell using poly[N-9′-heptadecanyl-2,7-carbazole-alt-5,5-(4′,7′-di-2-thienyl-2′,1′,3′-benzothiadiazole)] (PCDTBT) by as much as 29% but produced no enhancement in a BHJ device using poly(3-hexylthiophene). The position of the positive polaronic state of the polymer was found to be crucial to the enhancement. A power conversion efficiency of 6.27% for a PCDTBT-based BHJ device was achieved by using a chlorinated ITO anode without the needs of using any modifying interlayer or optical spacer at the cathode.

Synthesis and Field Emission Properties of Diamond Microcrystalline-Aggregate Array

The diamond microcrystalline-aggregate array was fabricated by microwave plasma chemical vapor deposition (MPCVD) method. The ceramic with a Ti mental layer is used as substrate. The diamond array was evaluated by Raman scattering spectroscopy, x-ray diffraction spectrum (XRD), scanning electron microscopy (SEM). The field emission properties were tested by using a diode structure in a vacuum. A phosphor-coated indium tin oxide (ITO) anode was used for observing and characterizing the field emission. It was found that the diamond microcrystalline-aggregate array exhibited better electron emission properties. The turn-on field is only 1.1V/μm and a emission current density as high as 1mA/cm2 was obtained under an applied field of 3.3V/μm. The good field emission properties of the diamond microcrystalline-aggregate array are discussed relating to microstructure and electrical conductivity.

Top‐Emission Organic Light‐Emitting Diode with a Novel Copper/Graphene Composite Anode

AbstractThe relatively high sheet resistance of graphene compared with indium tin oxide (ITO) blocks the applications of graphene as transparent electrodes in organic light‐emitting diodes. A novel copper (Cu)/graphene composite electrode is presented and employed as the anode of a top‐emission organic light‐emitting diode with the structure of Cu/graphene/V2O5/NPB/Alq3/Alq3: C545T/Bphen: Cs2CO3/Sm/Au. The Cu/graphene composite electrodes are fabricated by growing graphene directly on Cu substrates via the chemical vapor deposition method without any transfer process. The maxima of current efficiency and power efficiency of a typical Cu/graphene composite anode device reach 6.1 cd/A and 7.6 lm/W, respectively, which are markedly higher than those of the control devices with a graphene anode, a Cu anode or an ITO anode. The low sheet resistance of the composite electrode, the high quality of graphene without any transfer process and the avoidance of wave guiding loss in glass or polyethylene terephthalate substrates result in the improvements of light emission efficiencies.

Very low resistance ZnS/Ag/ZnS/Ag/ZnS nano-multilayer anode for organic light emitting diodes applications

In this paper, design and simulation of conductive nanometric multilayer systems are discussed and optimum thickness of Ag and ZnS layers are calculated to reach simultaneously to high transmittance and low sheet resistance. The conductive transparent ZnS/Ag/ZnS/Ag/ZnS (ZAZAZ) nanometric multilayer systems are deposited on glass substrates at room temperature by a thermal evaporation method. The electrical, optical, and structural properties of these multilayers, such as sheet resistance, optical transmittance, and the root-mean-square surface roughness are obtained. High quality nanometric multilayer systems with sheet resistance of 2.7 Ω/sq and the optical transmittance of ~75.5% are obtained for the ZAZAZ system. Organic light emitting diodes (OLEDs) were fabricated and tested on the ZAZAZ anode. The ZAZAZ multilayer anode based OLED shows the performance comparable to that of the indium-tin oxide anode based OLED.